1. Field of the Invention
This invention relates to a current limiting circuit interrupter and particularly to such an interrupter having an insulating wedge.
2. Description of the Prior Art
Large short circuit currents result from the use of low impedance transformers and interconnected networks in modern low voltage a.c. power distribution systems. Today, fault currents in excess of 100 KA are common. Traditionally, high fault current protection has been provided by current limiting fuses in conjunction with circuit breakers. However in recent years a new generation of high speed electromagnetically driven, single and multiple break current limiting devices have been developed. These devices not only perform the functions of a circuit breaker and current limiting fuse, but are also resettable and reusable. These devices can also be effectively applied to motor control as well as power distribution systems.
A review of the patent and technical literature reveals a wide variety of current limiting design concepts. All schemes use the electromagnetic forces generated by the fault current to achieve rapid contact separation. Two major factors control how well current limiting occurs; namely, how quickly the contacts part after initiation of the fault current and how rapidly the impedance of the air-arc develops.
It is well known that effective current limiting requires rapid contact separation. The operation of the traditional circuit breaker was far too slow for current limiting. Over the years, two basic design schemes have been developed which meet this current limiting requirement. That is, a solenoid/kicker system and a repulsion design using two closely spaced contact arms. Both schemes use the electromagnetic forces generated by the fault current to achieve rapid contact separation. Of these two designs, the repulsion scheme is the most direct. In this design, the mass to be accelerated is minimized, thus attaining high contact separation velocities. A variety of current limiting design concepts utilizing electromagnetic repulsion are available in the patent and technical literature. Notwithstanding the foregoing considerations, a problem of rapid arc extinction remains.